Memory devices, such as NAND or NOR flash memory devices, dynamic random access memory devices (DRAMs), static random access memory device (SRAMs), or the like, are generally fabricated on semiconductor wafers. Each of these wafers typically contains a number of individual integrated circuit memory devices formed in rectangular areas known as dies. After fabrication, each die is separated, or diced, then packaged in a format suitable for the end user.
Before or after dicing and packaging, a manufacturer may test its integrated circuit devices as part of a quality program to improve end-use reliability. Such tests are generally performed on highly-specialized testing systems or tester hardware. Prior to dicing, tests may be performed by the testing system on each die of a semiconductor wafer in pattern. The tester hardware may test each die individually or it may test multiple dies concurrently. Subsequent to dicing, tests may be performed by the testing system on multiple packaged components in pattern. The tester hardware may test each component individually or it may test multiple components concurrently.
A typical NAND flash memory comprises a memory array that includes a large number of memory cells arranged in row and column fashion. Each of the memory cells includes a floating-gate field-effect transistor capable of holding a charge. The cells are usually grouped into blocks, e.g., 2048 blocks. Each block includes a number of rows, e.g., 32 rows, and each row may include one or more pages, e.g., two pages. Each of the cells within a block can be electrically programmed on an individual basis by charging the floating gate. The charge can be removed from the floating gate by a block erase operation. The data in a cell is determined by the presence or absence of the charge on the floating gate.
To guarantee the programming speed of a memory device to a customer, typical test methods usually involve determining a time it takes to program each page and comparing that time to a predetermined acceptable programming time for a page. For some conventional test methods, if the programming time for any one of the pages is longer than the predetermined acceptable programming time, the entire block is failed and is repaired. That is, an entire block may be failed and subsequently repaired for just one slow block. Such repairs increase manufacturing times that result in reduced yields. Moreover, the frequency of the repairs is highly dependent on variations in the fabrication process.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative test methods for determining programming speeds.